I am a machinist and picked this item up at a flea market. Believe me, I was amazed when I set this to a standard and got a reading within a .001th. The micrometer was sold by F.W. Woolworths in the 1950's. The anvil even has a screw adjustment. The threads for measuring are actually SAE fine, I would guess around a 32 thds/in. on a dia. of .312. Anyway, people I worked with were amazed that what we would consider to be a toy was of that quality.